Hatchery trout stand lesser chance of survival than wild counterparts

Fish bred in highly domesticated hatcheries face a slimmer chance of survival than those grown in their natural environments, according to research by the WSU School of Biological Sciences.

“This has been a big deal for 20 years. This is nothing new,” said Kristy Bellinger, a zoology doctorate student. “The salmon crisis is our dwindling populations of salmon and steelhead we have here in the Pacific Northwest. They used to return in the millions and now we’re only seeing hundreds, maybe thousands, of fish returning.”

Rainbow trout populations are dwindling and larger, hatchery-bred fish are part of the reason, Bellinger said. She conducts research under the supervision of Associate Professor Patrick Carter in a lab operated by Professor Gary Thorgaard.

The research considers the effects of domestication on the sprint speed of the trout. Bellinger said the highly domesticated fish were largest and slowest.

In order to test this, Bellinger placed the fish in a chute and startled them repeatedly over 10 to 15 weeks, recording their speeds. She studied several lines of fish that represented various degrees of domestication, including wild, moderately and highly domesticated trout.

Degrees of domestication were defined by the number of generations reared in a hatchery. Highly domesticated fish were reared in a hatchery for more than 100 years.

The downside of using larger fish as rootstock in hatcheries is that more meat makes the fish slower and thus more likely to become prey, Bellinger said.

“We still see these highly domesticated fish being pumped into our rivers,” she said.

Hatchery-bred trout are released into the wild when they are 1 year old, at which point they migrate to the ocean, but wild trout don’t normally migrate until the age of 2, Bellinger said.

Carter said domesticated fish might not be an ideal supplement to wild populations.

“This is another piece of the puzzle for hatchery managers to think about as they’re making decisions about how to augment natural populations of rainbow trout,” he said.

Hatchery trout that are bred to have similar characteristics to wild trout stand a better chance for survival, Bellinger said.

“We want to caution the hatchery system in general from using these highly, highly domesticated fish to supplement any endangered or dwindling wild populations because we don’t expect them to be able to survive,” she said.

Hatcheries commonly use salmon as rootstock but have begun to utilize other methods in an effort to sustain trout populations, Bellinger said.

“Their main goal was to pump out a bunch of fish for harvest,” she said. “Now, a lot of these hatcheries are trying to become more sustainable.”

One hatchery built a side channel off of a stream for rearing trout in more natural conditions, she said. Other hatcheries let fish fully develop for two years before releasing them.

Some hatcheries expose trout to a predator before they are released, she said. The predator makes an example of some fish in the hatchery, training the others for survival in wild circumstances. Some hatcheries instead introduce predator pheromones that trigger similar behavior.

Trout that migrate to the ocean and return to fresh water, called anadromous trout, are important for the ecosystem because they deliver marine-derived nutrients to stream environments, which are nutrient-poor, Bellinger said. She said large salmon populations have brought nutrients to streams on the west coast and are partly responsible for feeding sequoia trees along the water’s edge.

“Historically they’ve been such an integral part of the ecosystem,” she said.

Thorgaard said few researchers have studied the effects of burst swim speed in trout.

“(Bellinger) provided one of the most thorough studies of this type of trait in trout,” he said.

Bellinger’s study was published in January in the Journal of Aquaculture.